Heavy Metals, Vitamin D, and Bone Content in Older Adults: An NHANES Analysis

This cross-sectional study examined associations between environmental heavy metal exposures (total mercury, inorganic mercury, blood cadmium, blood lead, and non-arsenobetaine urinary arsenic), vitamin D metabolites (25(OH)D₂ and 25(OH)D₃), and anthropometric variables with total femur bone mineral content (BMC) in a middle-aged to older adult cohort (aged 45–80 years; n = 541 with complete data) drawn from the National Health and Nutrition Examination Survey (NHANES) 2009–2010. The full analytic sample comprised 541 participants (mean age = 59.33 ± 10.33 years; 49.3% male; mean BMI = 28.33 ± 5.39 kg/m²; mean total femur BMC = 35.58 ± 9.75 g). Multiple linear regression analyses were conducted adjusting for age, sex, BMI, and urinary creatinine. The overall model explained 60.6% of variance in total femur BMC (R² = .606, adjusted R² = .598, F(11, 528) = 73.896, p < .001). Sex (β = −0.758, p < .001) and BMI (β = 0.303, p < .001) were the strongest determinants, with males exhibiting significantly higher absolute BMC than females. Total blood mercury demonstrated a significant negative association with femur BMC (B = −0.183, 95% CI [−0.359, −0.007], p = .041), while inorganic mercury was not significant (p = .825), suggesting the deleterious skeletal effect is driven by the organic (methylmercury) fraction. Total urinary arsenic initially showed a positive association; however, when seafood-derived arsenobetaine was subtracted to isolate the toxic fraction, this association completely disappeared (p = .258), confirming it as an artifact of dietary confounding rather than a direct protective effect. Neither vitamin D metabolite reached statistical significance. These findings underscore the importance of distinguishing mercury species and highlight total mercury as an independent predictor of reduced bone mineral mass in middle-aged and older U.S. adults.